Tracking antenna with anti-backlash spring in gear train

ABSTRACT

A steerable aerial, driven via a differential and two reduction gearboxes, on which backlash is eliminated by a spring biassing arrangement. The spring biassing arrangement is connected between the cage member of the differential and one of the planet gears of the differential and provides a constant torque spring bias to one of the reduction gearboxes in relation to that of the other.

United States Patent Cresswell [4 1 May 23, 1972 [54] TRACKING ANTENNAWITH ANTI- [56] References Cited BACKLASH SPRING IN GEAR TRAIN UNITEDSTATES PATENTS 72 Inventor: Richard Cremweil Essex, En and 1 813,396,594 8/1968 Walker ..74/409 [73] Assignee: The Marconi CompanyLimited, London,

England Primary Examiner-Eli Lieberman 22 Filed: Mar. 10, 1971 Attorner-Wight & Brown A steerable aerial, driven via a differential and tworeduction [30] Foreign Appuufio'? Priority Data gearboxes, on whichbacklash is eliminated by a spring Mar. I3, 1970 Great Britain..12,079/70 biassing arrangement. The spring biassing arrangement isconnected between the cage member of the differential and one [52] US.Cl ..'....343/765, 74/409, 74/410 of the planet gears of thedifi'erential and provides a constant [5 I] Int. CI. I .7 ..H01q torqugto one of the reduction gearboxes in rela.

tio n tothatofthe other; 343/762-766 5Claims,2DrawingFiguresPATENTEDMMNWZ 3,665,482

SHEET 1 BF 2 ANGLE AXIS WmZni wax/m $160M BY x 5111070 This inventionrelates to steerable aerial installations. One of the most importantexamples of such an installation is that in which an aerial is requiredto track a target such as a satellite. A satellite tracking aerial isrequired to track a target such as a satellite. A satellite trackingaerial is required to track its target with great accuracy, arequirement which also applies to other steerable aerial installations.A satellite tracking aerial is, as is well known, required to move inelevation and hour angle. The driving gear for hour angle movementcommonly comprises a bull gear carrying the so-called hour angleplatform, i.e. a platform from which the aerial is carried and, forobvious practical reasons, there has to be a large reduction gear ratiobetween the driving motor and the pinion or pinions actually engagingthe bull gear. For example, a quote a practical figure, the reductiongear ratio between motor and pinion may be over 3,000 to l.

Backlash or play in the gears is a source of great difficulty ininstallations as just described because even a very small amount ofbacklash or play is magnified in dependence upon the above gear ratio.Although it is well known to counter backlash or play by providing biasspringing between two meshed gears, this expedient does not provide asatisfactory means of countering such backlash or play between a pinionand a bull gear if the pinion is driven through a high reduction ratiogearbox. To quote again a practical figure the amount of backlash orplay to be expected in practice between a pinion and a bull gear, thoughsmall enough measured at these gears may be equivalent, measured at thedrive shaft to the reduction gear box, to as much as three whole turnsof that shaft and it will be apparent that spring biassing of the pinionwith respect to the bull gear does not provide a satisfactory solutionin a case such as this.

The present invention seeks to overcome the above mentioned difficultiesby simple and relatively inexpensive means which shall be purelymechanical in nature and do not involve the cost of providing anumber ofmotors, specially arranged and fed to exert different ratios of torquefor the mere purpose of taking up backlash or play. i

According to this invention a steerable aerial installation includes adriven gear from which the aerial is carried; a pair of driving gearsengaging said driven gear to drive the same; a pair of high reductionratio gearboxes each in the drive to one or other of said driving gears;a differential having driving means driven by a source of driving powerand a pair of differentially related driven means each driving one orother of said gearboxes; and spring bias means arranged to providesubstantially constant bias of the drive to one gearbox with relation tothat to the other.

Preferably, the differential is of the sun and planet gear wheel typeand provides the drives to the gearboxes from the shafts of its sunwheels. Preferably also the spring bias means is a spring operativelyconnected between the cage member of the differential and one of theplanet gear wheels of the differential.

The invention is illustrated in the accompanying drawings in which FIG.I is a general schematic perspective view of one form of steerableserial installation in accordance with the present invention and FIG. 2is a similar perspective view to a larger scale in more detail of thedrive arrangement of FIG. 1.

' Referring to FIG. 1, l is an aerial reflector mounted on a platform 2.This reflector is illuminated by a primary radio source indicatedconventionally at R and carried by supports S. The platform 2 ispivotally mounted about an elevation axis 3 in a U shaped bracket 4 onan hour angle platform 5. The hour angle axis is indicated by the brokenline so referenced. The movement of the aerial reflector 1 about theelevation axle 3 is provided by a jack arrangement consisting of a screw6 connected in trunnions 7 at one end to the platform 2, and a nutmember 8 which is on the screw and is rotatable b means not shown. AsWIII be apparent, when the nut mem r 8 is rotated the screw 6 is movedendwise and the aerial reflector is moved in elevation, i.e. about theaxis 3. The hour angle platform 5 is driven about a fixed tower 9 by amotor 10 via, in the order stated, a differential gear 11, two beveldriving gears 12, two reduction gear boxes 13, two driving gears 14, adriven gear 15 and a shaft 16. This gearing is mounted in a housing 17supported on the fixed tower 9. For simplicity, this gearing is notshown in detail in FIG. 1 only the parts 14, 15 and 16 are indicated inFIG. 1 but is shown in some detail and to a larger scale in FIG. 2 whichwill now be described.

Referring to FIG. 2 the motor 10 drives via a belt 18 the cage member 19of a differential 11 the sun or output gear wheels 20 of which drivethrough shafts 22 and bevel gears at 12 the two reduction gear boxes 13.The differential planet wheels driving the sun wheels 20 are referenced21.

A substantially constant torque spring 23 operatively connected betweenthe cage member 19 and one of the planet gear wheels 21 is arranged toprovide a substantial constant torque spring bias of the drive to one ofthe gearboxes 13 in relation to that of the other.

The gear boxes 13 are designed to provide a high reduction gear ratio (apractical although not limiting value being of the order of 3000 l) inthe drive to the driven gear wheel 15 through the pinion gear wheels 14.The directions of rotation of the shafts and gears is indicated byarrows.

I claim:

1. A steerable aerial installation including a driven gear from whichthe aerial is carried; a pair of driving gears engaging said driven gearto drive the same; a pair of high reduction ratio gearboxes each in thedrive to one or other of said driving gears; a differential havingdriving means driven by a source of driving power and a pair ofdifferentially related driven means each driving one or other of saidgearboxes, and spring bias means arranged to provide substantiallyconstant bias of the drive to one gearbox with relation to that of theother.

2. An installation as claimed in claim 1 wherein the differential is ofthe sun and planet gear wheel type and provides the drives to thegearboxes from the shafts of its sun wheels.

3. An installation as claimed in claim 2 wherein the spring bias meansis a spring operatively connected between the cage member of thedifferential and one of the planet gear wheels of the differential.

4. An installation as claimed in claim 3 wherein said aerial is carriedfrom said driven gear by means of a carrier member which is carried byand rotates with said driven gear on the axis thereof, said aerial beingpivotted to said carrier member about a pivotal axis perpendicular tothe axis of said driven gear and means being provided for adjusting theangular position of said aerial with respect to said carrier memberabout said pivotal axis.

5. A satellite tracking aerial installation in accordance with claim 4wherein the axis of rotation of said driven gear is the hour angle axis.

1. A steerable aerial installation including a driven gear from which the aerial is carried; a pair of driving gears engaging said driven gear to drive the same; a pair of high reduction ratio gearboxes each in the drive to one or other of said driving gears; a differential having driving means driven by a source of driving power and a pair of differentially related driven means each driving one or other of said gearboxes, and spring bias means arranged to provide substantially constant bias of the drive to one gearbox with relation to that of the other.
 2. An installation as claimed in claim 1 wherein the differential is of the sun and planet gear wheel type and provides the drives to the gearboxes from the shafts of its sun wheels.
 3. An installation as claimed in claim 2 wherein the spring bias means is a spring operatively connected between the cage member of the differential and one of the planet gear wheels of the differential.
 4. An installation as claimed in claim 3 wherein said aerial is carried from said driven gear by means of a carrier member which is carried by and rotates with said driven gear on the axis thereof, said aerial being pivotted to said carrier member about a pivotal axis perpendicular to the axis of said driven gear and means being provided for adjusting the angular position of said aerial with respect to said carrier member about said pivotal axis.
 5. A satellite tracking aerial installation in accordance with claim 4 wherein the axis of rotation of said driven gear is the hour angle axis. 